The subject matter disclosed herein relates to the fabrication and use of radiation detectors, including X-ray radiation detectors, having integrated electronic readout circuitry and capable of generating both photon-count and integrated-energy data.
Non-invasive imaging technologies allow images of the internal structures or features of a subject (patient, manufactured good, baggage, package, or passenger) to be obtained non-invasively. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the internal features of the subject.
Computed Tomography (CT) scanners typically operate by projecting fan-shaped or cone-shaped X-ray beams from an X-ray source. The X-ray source emits X-rays at numerous view angle positions about an object being imaged, such as a patient, which attenuates the X-ray beams as they traverse the object. The attenuated beams are detected by a set of detector elements which produce signals representing the intensity of the incident X-ray beams on the detector. The signals are processed to produce data representing the line integrals of the linear attenuation coefficients of the object along the X-ray paths. These signals are typically called “projection data” or just “projections”. By using reconstruction techniques, such as filtered backprojection, useful images may be formulated from the projections. The images may in turn be associated to represent a volume or a volumetric rendering of a region of interest. In a medical context, pathologies or other structures of interest may then be located or identified from the reconstructed images or rendered volume.
Conventionally, radiation detectors can operate in an energy-integrating (i.e., readout of the total integrated energy deposited during an acquisition interval) mode or a photon-counting (each individual X-ray photon is detected) mode. Conventional scintillator-based photon-counting modes utilize silicon photomultipliers (SiPMs) that are expensive and not practical for high count rate applications such as CT. Thus, energy integration is the conventional mode for reading out X-ray detectors in most clinical applications. However, energy-integrating readout approaches operate poorly in low-flux imaging applications, where electronic noise associated with the detector readout operation may overwhelm the available signal. Further, in some applications, photon counts are of more interest than the total integrated energy information associated with energy-integrating approaches.